1. Field of the Invention
The present invention relates to a determination device, a determination method, and a determination program.
2. Description of the Related Art
In the conventionally known technology of vehicle navigation (hereinafter also referred to as “navigation”), a vehicle that a user is on board is navigated to a destination by using a mobile terminal device such as a smartphone. Such a terminal device that performs navigation specifies the current position of the vehicle by using a satellite positioning system such as the Global Positioning System (GPS), and displays the specified current position and a screen illustrating a map and a route in an overlapping manner.
However, the terminal device is unable to display the current position at places where it is difficult to receive signals from satellites, such as inside of a tunnel. This problem is not limited to the GPS but also occurs to general positioning technologies using external signals (for example, radio waves from a mobile phone (cellular) base station, and wireless LAN radio waves). For this problem, the autonomous positioning technology is available that estimates the current position of the vehicle based on acceleration measured by an acceleration meter. For example, in a disclosed method, a device including an acceleration meter is fixed inside the vehicle in a predetermined orientation, and the traveling state of the vehicle is determined based on acceleration detected by the device.
Patent Document 1: Japanese Patent No. 4736866.
However, a terminal device such as a smartphone has a different in-car installation orientation depending on, for example, the type of a car that a user is on board and the use condition of a holder holding the terminal device, and thus it is difficult to determine the traveling state of the vehicle in some cases.
For example, the terminal device includes an acceleration meter that detects acceleration in an axial direction with respect to the terminal device, and converts the direction of the detected acceleration into a direction with respect to the traveling direction of the vehicle based on the installation orientation of the terminal device. Then, the terminal device specifies the traveling direction and speed of the vehicle by using acceleration in the converted direction, and specifies the current position of the vehicle based on the specified traveling direction and speed. However, the terminal device is unable to convert the direction of the acceleration when the installation orientation is unknown or has changed, which degrades the accuracy of determination of the traveling state.